Voltage regulators are commonly used in electronic devices to maintain a load current at a specified proper voltage level for powering the various electronic components of the device. In a typical low dropout voltage regulator, the load current is passed through a power transistor (a pass element) that is regulated by a feedback loop (a control circuit) that ensures the voltage level output by the power transistor is held relatively constant. The control circuitry that regulates the operation of the power transistor is typically contained in an integrated circuit (IC). The power transistor, however, may or may not also be contained in the integrated circuit along with the other circuitry.
FIGS. 1 and 2 illustrate the two general voltage regulator design types. FIG. 1 shows a voltage regulator 100 with an IC 102 having an internal power transistor 104, and FIG. 2 shows a voltage regulator 106 with an IC 108 connected to an external power transistor 110. In either case, the voltage regulator 100 or 106 supplies power at a regulated output voltage level to a load represented by a resistor 112 or 114 and a capacitor 116 or 118, respectively. Feedback loops (generally involving functions such as those of amplifiers 120 and 122, feedback voltage dividers 124 and 126 and reference voltage generators 128 and 130 interconnected as shown) that control or regulate the operation of the power transistors 104 and 110 are very similar to each other in concept. However, whereas the IC 102 has an input node 132 to provide the supply voltage to the internal power transistor 104 and an output node 134 for the output voltage from the internal power transistor 104; the IC 108 has an output node 136 for a control signal from the amplifier 122 to the external power transistor 110 and an input node 138 to provide feedback of the output voltage into the IC 108.
Sometimes, whether an electronic device maker uses an internal power transistor or an external power transistor may be simply a matter of design choice. However, the choice is often constrained by other design requirements. For instance, voltage regulators of the second design type (with the external power transistor 110) typically are better able to handle greater load current levels than are voltage regulators of the first design type (with the internal power transistor 104). Additionally, voltage regulators of the first design type are typically smaller than voltage regulators of the second design type. Other differences can also constrain the design choice. Therefore, the two design types are usually not interchangeable.
In either of the voltage regulator design types, some form of frequency compensation scheme must be implemented to ensure proper functioning of the voltage regulator (e.g. 100 or 106) and of the electronic components powered thereby. Due to the differences in device parameters of the internal and external power transistors (e.g. width/length ratio, threshold voltage, transconductance, gate capacitance, etc.), which can be different by several orders of magnitude, among other considerations, the potential frequency compensation schemes for one design type are generally incompatible with the other design type. Therefore, the designs for the different types of voltage regulators (e.g. 100 and 106), and the ICs (e.g. 102 and 108) used therein, must implement very different and non-interchangeable frequency compensation schemes.
As a consequence of the inherent differences between the two general voltage regulator types and the relative advantages and disadvantages of each, it is necessary for designers and manufacturers of the voltage regulator ICs (e.g. 102 and 108) to produce at least two different voltage regulator ICs (or families of voltage regulator ICs), so they can satisfy their customers' needs for either type of voltage regulator circuitry, since the same voltage regulator IC cannot be used in both types of applications, even though either design type could conceivably be used in some of the same electronic devices. In other words, the designers and manufacturers of the voltage regulator ICs must maintain availability of at least two SKUs (stock keeping units) for multiple products that are somewhat redundant in spite of being of incompatible and non-interchangeable designs. As is usually the case, however, larger numbers of SKUs generally lead to lower efficiencies in resource utilization and inventory management and, thus, higher costs for each SKU.